Printheads for inkjet printing systems often incorporate one or more ejection chips that include a layered semiconductor wafer substrate that is processed and/or treated to define structures for use in the thermal ejection of liquid ink from the printhead onto a medium, such as paper.
In some inkjet printing systems, a patterned plate forms the outermost layer of the ejection chip, and includes at least one nozzle aperture through which ink is ejected. Accordingly, ejection chips incorporate one or more interior pathways through which liquid ink flows prior to thermal ejection through the nozzle.
The degree of hydrophobicity and hydrophilicity, i.e., the affinity to repel or attract fluids, respectively, of portions of an ejection chip plays an important role in the overall performance of the ejection chip. For example, as the size of nozzles in nozzle plates shrink in order to achieve smaller ink droplet sizes, the sensitivity of the fluid ejected to the surface energy of the nozzle plate increases dramatically. One factor that may effect the ejection of fluids from the nozzle plate may be the accumulation of fluid or other contaminants on the nozzle plate surface. Such accumulation of fluid on the nozzle plate may adversely affect both the size and placement accuracy of the fluid droplets ejected from the ejection chip.
Further, it has been observed in operation of some inkjet printheads that the high temperatures and/or pressures associated with thermal ejection of liquid ink may result in the formation of bubbles of air or other gases within the ink as it travels along the interior pathways of the ejection chip prior to ejection. An abundance of such bubbles prior to thermal ejection of the liquid ink may result in sub-optimal performance of the inkjet printhead, for example, low printing quality, consistency, and/or density, to name a few.